Hi Giovanni,
You are correct in your assessment that this shader is trying to sample the depth buffer as a texture while it is the depth attachment to the active frame buffer. You should however be able to fetch the pixel’s depth using LookupDeviceZ(float2 screenUV) which performs a buffer fetch from either the depth buffer (if supported by the hardware) or from the depthAux which is a color target that mirrors the contents of the depth buffer in the forward renderer.
Best regards.